In this information age, virtually every home in the United States has one or more telephone lines for connecting telephone equipment to a public switched telephone network (PSTN) to realize voice communications. Each telephone line typically comprises a pair of copper wires forming a two-way communication path.
Telephone lines are traditionally distributed to a home from a central office, serving as a gateway to the PSTN, via a distribution cable composed of many plastic-insulated copper wires twisted together into pairs. Recently, to share facility to provide both cable television (CATV) service and telephone service, a coaxial cable was used to transport both CATV signals and voice communications between the central office and a home. The coaxial cable runs from the central office and is terminated at a network interface unit (NIU) outside the home, from which individual CATV and telephone lines extend into the home.
In either event, when the telephone equipment connected to any such telephone line is in use and conducts electricity, known as an "off-hook" condition, it draws current from the telephone line, referred to as "loop current," for voice communications. However, the amount of loop current available from the telephone line is limited.
It is common that a telephone line in a home is connected in a parallel manner to multiple telephones of different varieties, e.g., of different manufacturers and models, corded versus cordless, etc. The multiple telephones are sometimes used simultaneously by different users to participate in the same telephone conversation. In that case, each of the off-hook telephones draws loop current from the telephone line. Because of the limited loop current supply, one or more of the off-hook telephones oftentimes draw insufficient loop current, causing their audio level to drop significantly from the desired level, so much so that it may become undetectable. As a result, the user of one such telephone can hardly participate in the telephone conversation.
An obvious solution to the above-identified problem is to increase the limit of the loop current afforded by each telephone line. However, such an increase calls for a telephone company's adding facilities for supplying loop current to support the telephone lines serviced thereby, and each of such facilities is costly. The actual number of the additional facilities required depends on the number of the telephone lines in service, which is extremely large. As a result, such additional facilities represent a huge extra cost to the telephone company, and the above solution is thus not economically feasible.